The present invention relates to a video signal processing apparatus, and more particularly, to a video signal copying apparatus for copying a signal which has been recorded on a recording medium onto other recording media.
Generally, a video signal recorded on a video tape can be copied onto other video tapes using two video tape recorders or a dual-deck recorder.
According to a first method using two video tape recorders, one video tape recorder picks up a signal to be copied from a tape, and then outputs a demodulated signal via a general reproducing process such as demodulation. Also, the other video tape recorder receives the demodulated video signal and then records the video signal on a tape via a recording amplifier after performing a general recording process such as modulation.
According to a second method using a dual-deck recorder, a signal to be copied is picked up from a tape by a signal processing unit of a first deck and then a modulated signal is recorded on another tape by a signal processing block of a second deck directly without demodulation.
In the above second method, the signal modulation is omitted during the tape copy process compared to the first method, and the modulated signal picked up by a reproducing deck player is directly recorded on a tape by a recording deck recorder. Accordingly, the signal-to-noise (S/N) ratio is improved.
FIG. 2 is a block diagram showing the structure of a conventional video signal copying apparatus, illustrating an example of the video signal copy technology related to the above second method.
The prior art will be described with reference to FIG. 2.
The conventional video signal copying apparatus includes a luminance processor composed of a high-pass filter (HPF) 2010, a phase compensator 2020, an equalizer 2030 and a limiter 2040, a color processor composed of a low-pass filter (LPF) 2100, a voltage-controlled amplifier 2110 and a switching unit 2120, an automatic color gain controller composed of a demodulator 2050, a synchronous signal separator 2060, a burst gate signal generator 2070, a color signal determiner 2080 and a peak level detector 2090, and a mixer 2130 for mixing the processed luminance and color signals.
In a color signal process, an automatic color gain control (ACC) circuit is used to control the degree of color saturation, maintaining a color level at a predetermined level.
The ACC circuit separates only a burst signal from an input color signal and then detects the level thereof to thereby maintain a constant level, so that the gain of the color signal is controlled to a predetermined level.
The ACC circuit performing the above operation normally operates even when a black and white signal is input. The ACC circuit amplifies a black and white signal corresponding to a frequency band of a color signal to the maximum gain, resulting in a saturated signal.
When the black and white signal is input as above, a color signal determiner 2080 for determining whether a color signal exists or not outputs a color killer signal to a switching unit 2120 to prevent the output of the signal ("color band signal") corresponding to the frequency band of the color signal after the color band signal is amplified to the maximum gain.
When a black and white signal is input, the conventional ACC circuit amplifies the color band signal to the maximum level and then blocks the output thereof. As a result, a luminance signal corresponding to the frequency band of the color signal is also prevented from being output, so that the frequency band of the luminance signal decreases as shown in FIG. 4C, thereby lowering picture quality.